It is the best in the market at this price, at 550 euros it's almost a steal.
I have played for a long time with many of its "competitors" such as Yamaha 125, Kawai 110, Roland FP30, especially in terms of the keyboard, they don't stand a chance.
With the Korg D1, I immediately appreciated its sturdy construction, it gives you the feeling of playing on a professional stage piano.
The sound is a matter of personal taste, I personally really like it, but the sound of the Kawai 110 is also very good, while the Roland is digital and the Yamaha is indifferent.
It is very simple to use and everything is right in front of you without needing to enter menus or press any buttons to change the sound.
It may not have many sounds, but they are of high quality.
It does not have speakers, and it's better that way because they would be unnecessary weight. Besides, I consider speakers in this category to be simply useless. It's much better to play with good headphones or studio monitors (Yamaha).
I highly recommend it, although for some people the weight may be a disadvantage. I think it's around 16 kilograms, but it compensates with the excellent keyboard, which is also made in Japan.
I would also recommend combining it with the Korg sustain pedal DS1H with 2 positions because the one provided in the package is just a simple on-off switch.

We have it for only two days, we bought it for our daughter who is learning piano. Very easy to use and with a construction that shows it is solidly professional. Don't forget that you need two TRS plugs for connecting it to an amplifier or self-powered speakers. I bought two TRS male to RCA female because my amplifier had RCA connections. I haven't bought a stand yet, but it fits perfectly on an Ikea furniture.

Well, I have had the piano for 7 months now and I am completely satisfied. At home, we also have an fp10 Roland and a classic American Baldwin, and I play once a week on a very expensive (for an electric) Kawai CA78 of my teacher, so I can compare them. It has 30 high-quality sounds. It has a very good keyboard and incredibly weighted keys, RH3 keypad made in Japan (the same as the expensive Korg Kronos). They have a very good feel without being too hard like the Roland (which is quite good but overall not as professional) and it closely resembles a classic piano. It can easily interpret anything someone knows. The pedal that comes with it is perfect, and optionally it can also take another pedal with two levels of sustain sensitivity. Its sound is flawless and it has some settings like reverb, chorus, and brilliance. It is a professional stage piano. Attention, it does not have built-in speakers so you have to connect it to your own, whether it is an old home cinema system, computer speakers, hi-fi, studio monitors, etc. Furthermore, it has two Jack outputs and a mini-jack for headphones in the front. However, keep in mind that for the same price, other electric pianos with built-in speakers do not have any amazing speakers to leave you speechless... Choose this one, it is also very beautiful and elegant. Look for reviews on YouTube and you will see that everyone says the best things.